This invention relates to an improved transmission. It may be considered an improvement on the hydromechanical transmission described in U.S. Pat. No. 3,888,139 which issued June 10, 1975, to Elias Orshansky, Jr.
The transmission of U.S. Pat. No. 3,888,139, and the transmission of the present invention each provide a hydromechanical infinitely variable transmission. Each provides for improved utilization of vehicle engine power by enabling the engine to operate within a narrow speed range which has been optimized for minimum emissions, maximum fuel economy and maximum power, regardless of vehicle operating conditions.
In U.S. Pat. No. 3,888,139 the hydraulic units used as a speed-varying means were driven by gears from either the input or the reaction or both. The present invention eliminates those gears, four gears altogether, and their bearings, thereby reducing the size and weight of the transmission and reducing the cost of the transmission.
It is also an object to provide a transmission which can weigh less than conventional transmissions.
The transmission of this invention may have a concentric or coaxial construction or may have a transverse construction. It has an entirely different hydrostatic start from the transmission of U.S. Pat. No. 3,888,139, in order to provide reduction in the number of parts, the size, the weight, and also the cost of the transmission.
In order to avoid having to use the extra gears which connected the planetary assemblies to the hydraulic units in U.S. Pat. No. 3,888,139, the hydraulic units in one form of the present invention are especially designed to be installed in line with the planetary assemblies without a separate gear drive. This considerably reduces power losses, size, weight, and cost. However, there are sometimes advantages in transverse construction, and in another form of the invention using such transverse construction cost savings in the hydraulic units become feasible.
The invention may also be considered an improvement over our co-pending application Ser. No. 787,851, filed Apr. 15, 1977, which requires three planetary assemblies; all of which have the sun gears on a common shaft.
A conventional torque converter or manual transmission requires the imposition of many compromises upon the engine, because it must provide adequate performance over a wide range of torque and speed. The practice of most vehicle manufacturers of providing a selection of optional axle ratios for the vehicle is only one of the many attempts which have been made to reduce the compromise for any given application.
The infinitely variable transmission of this invention enables the engine to be operated at all times in a speed range in which it is capable of producing rated power. Therefore, vehicle performance in any given application can be maintained or even improved while utilizing a smaller engine. In contrast, infinitely variable transmissions of the pure hydrostatic type are limited to applications where significant power losses can be tolerated in return for the benefits of improved transmission ratio control.
Hydromechanical transmissions offer the control benefits of hydrostatic transmission, and, since only a portion of the engine power is transmitted by the hydraulic units, they provide a means for removing the performance barrier of excessive power losses. The extent to which any hydromechanical transmission can accomplish this is a function of the percentage of power which must be transmitted hydraulically.
The new transmission hereof can transmit high horsepower over a wide range of output speed variation at a constant input speed and horsepower. It differs from the previous transmissions in its ability to transmit power over a wide range with a minimum of transmitted hydraulic horsepower, and a minimum of installed hydraulic horsepower. It also provides full engine braking over its entire range of operation.
The invention avoids the pitfalls of excessive complexity, speeds, or loads in the gear train. Simplicity of construction and conventional gear ratios and proportions help to hold cost down. Maximum reliability and minimum cost have been obtained by utilizing standard commercial hydraulic unit design practice which enables operation totally within long-life rated conditions of speed and power. In addition, the clutches can utilize the same low-cost paper elements presently employed in high production automobile torque converter transmissions. For a comparable power rating, a smaller number of elements than in a torque converter power shift transmission can be utilized, because at all shift points the clutch elements are virtually synchronous. The number of elements is, therefore, a function not of their thermal capacity, but of their steady-state torque capacity.
This new transmission is valuable for use in passenger and competition cars, highway and off-highway trucks, buses, agricultural and construction equipment, military vehicles, and industrial drives and machine tools.
The use of this transmission in a piston-engine vehicle enables reduction of exhaust emissions and improvement in the specific fuel consumption by programming the engine to operate within its optimum range under all road conditions without regard to transmission torque output requirements. Both hydrocarbon and nitrogen oxide emissions can be minimized by optimizing the engine for operation in a specific narrow range. In addition, a smaller engine may be utilized for any application, as the transmission enables full engine power to be developed at any vehicle speed except for the lower speeds where the vehicle is traction limited. It is particularly desirable to operate turbocharged diesel engines in a narrow range of speed.
Rotary combustion engines can use this new transmission with the same advantages as for piston engines. The benefit in reduction of hydrocarbon emissions is there of a much greater magnitude, however, due to the high rate of change in emission characteristics for rotary combustion engines with respect to engine speed.
Gas turbines would also be benefited significantly by this invention. Manufacturing cost is a major drawback in producing a turbine today. This, to a large degree, is a function of the complexity required in the design of a turbine for use under the varying torque and speed conditions of a road vehicle. With the hydromechanical transmission of this invention, the transmission can be programmed to operate the turbine only under these conditions during which it is most efficient. Therefore, a single-shaft turbine becomes feasible, as it is more economical to manufacture than the two-shaft design normally proposed for vehicle application. Since constant-speed operation is feasible, the problems in connection with the throttle response time of a turbine do not arise. Because there is an infinite variation in speed and torque in the transmission, and no interruption of power flow occurs at any time, the turbine design speeds can be maintained.
Another important feature of the invention is the provision of gear proportioning so that the hydraulic horsepower on both sides of the shift is the same. This means that the efficiency of the transmission is nearly the same on each side of the shaft points, and, therefore, the control system can be greatly simplified.